


Illya's Birthday Surprise

by Gothdresser



Category: Fate/kaleid liner PRISMA ILLYA
Genre: Birthday, Desperation, F/F, Grinding, Omorashi, Premature Ejaculation, Scat, Soiling, Wetting, diapermessing, dirty diaper, facesitting, messing, peeing, pissing, pooping, poopy panties, urinating
Language: English
Status: Completed
Published: 2020-08-27
Updated: 2020-08-27
Packaged: 2021-03-07 02:21:51
Rating: Mature
Warnings: Underage
Chapters: 1
Words: 5,410
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/26139586
Author URL: https://archiveofourown.org/users/Gothdresser/pseuds/Gothdresser
Summary: A bit late but I've had it lying around for almost a month now as well. Chloe ropes Miyu into a surprise present for Illya which turns out to be pretty intimate for Illya and Miyu.
Relationships: Miyu Edelfelt/Illyasviel von Einzbern
Comments: 2
Kudos: 5





	Illya's Birthday Surprise

With her heels landing on a certain bedroom floor of the house across the street, the kaleidostick dispelled from the raven-haired girl, although Miyu still shifted a little nervously in place. Today was her birthday, the same as the other girl in the room, as well as her best friend who surprisingly wasn’t in her own room. “Chloe, I know you asked me to help you with a gift for Illya, but don’t you think the evening on her birthday is a little too soon? Like what are we even supposed to do when it’s so late and Illya could come in here at any moment?” Maybe she really should have bought Illya a gift anyway, but Chloe was so vehement about them making a gift together.

The young brown-skinned girl wasn’t without her surprises though. “I told you I had this covered but that you were the most important part for making the gift work. This will be her favorite gift ever if she got it from you~” It was just enough of a tease as Chloe noticed Miyu’s interest piquing before she dragged out a large gift box from behind the bed, as well as a small bag with a party store’s logo. She pushed the bag into the other girl’s hand though as she moved close up to her ear to whisper exactly what the surprise was going to be.

To say that Miyu was shocked was an understatement, but she kept focusing on the most important line that Chloe said: “Doing this will make Illya love you forever.” No matter how much she wanted to give the bag back and refuse such a ridiculous idea, something stirred in Miyu as she couldn’t resist the thought of Illya loving this gift so much. Even she knew that this would flick Illya’s switch despite not being the usual trigger of her maid outfit, and so her dark hair swished a little from a few bobs of her head. She had to go along with this idea, it was just too perfect of a chance that she couldn’t resist.

With a small wave back to Chloe as Miyu was left by herself in the room, she held her breath and pulled out a pair of objects from the back. A gift bow and some ribbons were often used for birthday parties, but it almost felt like she was violating the sanctity of a birthday when using these items in such a depraved manner. Still, this was for Illya and so Miyu’s shorts dropped to the floor before she removed them from her ankles. Her shirt came off right after, leaving her in only her matching dark blue panties and bra, but as per Chloe’s instructions, that bra was tossed in with the rest of her removed clothes.

As those went in the bag, the ribbon was unspooled while Miyu did her best to think of how to wrap it around herself, constructing a sort of replacement bra out of the red ribbon around her chest. More of it went lower and lower down her chest and stomach, leading to wrapping a bow around her abdomen out of the ribbon, before cutting it off with some scissors from Illya’s desk. The ends of the ribbon draped over a small growing bulge in her panties as while this was quite embarrassing, Miyu could feel her heart racing from the fact that she was doing this for Illya. To finish off the gift, she put the premade ribbon on top of her hair and stepped inside the box. She really couldn’t believe she was going along with it but it was Illya’s birthday, after all.

Miyu then grabbed the top of the box, lowering it into place as she squatted into the box herself, seeing a pair of much smaller boxes before sealing herself off. Did Chloe really get something else while telling her not to… If she did, then Miyu was going to have a strong word for her, but for now, she trusted in the pervert’s perverted plan, although how long did she say she was going to have to wait again? Chloe only mentioned something about cake cutting, so that wouldn’t take very long and if only she had taken her phone with her to pass the time.

Maybe it was taking much longer than she expected, or perhaps being in the box like this messed up her perception of time, but Miyu found herself waiting what felt like an hour, even if it may have only been five minutes. It was all just so tough to tell but every time that she considered lifting up the top of the box, she was afraid that Illya would walk in and she’d ruined the surprise. This was going to be so good and Chloe’s words still rang in her mind, forcing herself to stay in the box despite something else making the time feel like it was passing even slower.

In all of this excitement, Miyu hadn’t really considered the fact that she’d be waiting in here for what might be an extended duration, so she hadn’t thought of relieving herself in terms of a pair of important needs. Not only did Miyu have to pee, but somehow the need to poop was even worse. Why did it have to start poking a little now of all times, but Miyu had to keep holding it in, obviously not wanting to soil the surprise in such a manner. Plus, a fifth-grader wasn’t supposed to have accidents, and yet as time slowly ticked by, Miyu began wondering if she’d have to forsake that.

What would Illya think of her pooping herself though, and just as Miyu crafted the plan to try to rush to the bathroom, she barely managed to lift the lid of the box before hearing the sound of the door handle turning. Oh, if only she had done it earlier or they had been delayed by a few more minutes, but Miyu quickly replaced the top of the box. Maybe that was just a little too much of a surprise as she felt the front of her pants dampen just a little, a warm wet feeling on her bulge down there. Did she actually… please let it dry, please let it dry, please let it dry…

Her anxiousness was only made worse as she could hear the muffled sounds of Illya and Chloe from outside of the box, namely Chloe introducing the various gifts she had gotten for the birthday girl. Maybe Chloe really had duped her in this fashion, although Miyu’s thoughts were quickly interrupted as she accidentally let out a loud fart. Loud enough that she even heard Illya ask about it, only making Miyu even more nervous as the poop peeking out of her ass was much harder to keep in. Oh no, she couldn’t, not now, not when Illya w-was…

Try as she might to keep holding onto the mess, the dark-haired fifth-grader was unable to resist the pressure in her bowels as she felt her ass start to slowly be spread by a huge mess, desperately trying to hold on as she was completely distracted by her accident. That speed changed though as suddenly the box was swathed with light, and Miyu could only whimper as she looked Illya in the eyes, an excited look on the silver-haired girl’s face as Miyu lost complete control of her bowels.

The nearly-naked girl loudly groaned while crackling and squishing and mushing erupted from her ass, a large load of shit filling up her panties almost completely. There was even so much that it stretched out the dark blue fabric, staining just ever so slightly darker with the pressure of so much crap pressing against it. Miyu absolutely couldn’t believe that she just soiled herself in front of Illya, of all people, and so very loudly too as she squished a little a few times more while her bowels made sure she was completely empty.

As soon as her butt had finished with all of its embarrassing and disgusting sounds, Miyu shakily stood up inside the box, her legs shivering as she could no longer meet Illya’s eyes. She didn’t even really want to look at Illya’s face right now, absolutely afraid of her best friend being repulsed by such a display. There was just no excusing this, and all Miyu tried to weakly say was, “Happy b-b-birthday, I-Illya…” On top of it all, the sound of liquid hit the cardboard of the box she was in as Miyu’s bladder finally gave up trying after having already shamed her so much already, the warm golden liquid making a more obvious dark spot on her little bulge before streaming down her legs and pooling a little at her feet. If only she made the ends of the ribbon a little long since instead of hiding her crotch, the pair of ends of the bow instead framed the obviousness of her accident. “S-sorry for ruining your bi-”

All of a sudden, Miyu found a pair of hands around her wrists, raising them up so she couldn’t stop herself from seeing Illya’s disappointed face. Or, well, that’s the kind of face she expected, but instead, Miyu recognized a different look in Illya’s eyes. It was like the first time seeing her in a maid dress but sort of more intense, especially since Miyu swore she could see Illya drooling a little too. The question of if Illya was actually into this kind of thing came to mind, reinforced more when she stole a glance at Chloe to see quite the smug look on her face. Had she planned this the whole time?

The time to wonder was long past though since Illya had Miyu on more of a display now, excitedly shaking in place as her eyes kept going up and down the nearly-naked body, but more so with looking around her. “I didn’t think you’d go this far for my birthday, b-but…” Her body shifted back and forth as she bit her lip, almost as if she was having trouble deciding what to do first with her messy friend. There were so many options and with how far Miyu had gone already, there was little that’d make her turn back now. “Well, it didn’t look like you meant to have an accident, so I’d feel bad for making you stay in it, even if I… No, is it alright to help you clean up, Miyu? I promise I’ll be gentle and think of it as a birthday gift for you.”

“O-oh yeah, of course, but you don’t need to worry about that. Just please be gentle, like you said.” Miyu’s mind was feeling pretty jumbled at this point as so much was happening so quickly and she couldn’t help but notice that the look in Illya’s eyes was still there. She hadn’t reacted like the maid outfit though which calmed Miyu but still only a little as Miyu looked for a place to settle down. Just the thought of lying on her back made her feel pretty infantile, so she instead elected to bend over with Illya’s bed as support, letting the large mess settle and sag against her upper thighs. “Does th-this work for cleaning me up?”  
Miyu got a much different answer than she was expecting though as she heard a soft groan behind her but before she could turn around, Illya’s skirt was already off, leaving her in only a shirt as something was strongly pressing the mess against more of her butt. “Oooh, that’s just perfect but you really are giving off some mixed signals, Miyu. One minute you have an accident and then you’re showing off your butt like this. Or was that not so much of an accident as you’re making it look like?”

And to think she picked this pose to feel less infantile but now she almost wondered if she was just doing this subconsciously. She had kept doing this because Chloe said Illya would love her forever, although this wasn’t quite the love she was expecting. “I told you, it was an accident. I’m a fifth-grader and a magical girl, I shouldn’t be s-soiling myself. If this is what you like though, I wouldn’t mind if you continue but uh… c-can we have some privacy please?”

With how intimately close the pair of girls already were, the only oddball in the room was quietly watching her sister mount their friend. “Fine, fine, and to think I was going to get a good show too. I’ll show myself out then but when you’re done, open the larger of the other two presents first. You’ll thank me later~” With that, Chloe made her way out of the room but not before oddly setting her phone down on Illya’s dresser with the back of the phone facing the pair of girls.

“I think I’m starting to get what you want a little more now though, Miyu. Even if you had an accident, you were still dressed up in all of this ribbon.” Her crotch was already grinding against Miyu’s big bulging loli butt again before Chloe closed the door, ramping up a little in speed against all that mushiness. Just doing this was already making the front of her panties tighten though, so she’d really have to hurry up if she wanted to stick it in. “Come on, tell me why you wanted to be my gift. Tell me a-all of, hnnngh!”

Illya’s crotch was pressed against Miyu’s butt enough already but the raven-haired girl felt Illya put more of her weight against her, coincidentally she felt something damp slowly drip down her butt and thighs. Just as she was starting to get into it herself though, and a glance back gave Miyu a look at Illya’s reddened face. Maybe she could better explain the gift thing afterward but Miyu now realized exactly what had happened, all because she had pooped her panties. “I-Illya, did you just… That was so fast.”

She hadn’t even been this quick during the maid incident, and yet Illya had to deal with the fact that she prematurely came on her best friend’s poopy panties. But, to be fair, Miyu had really loaded them up and how could she resist that when it felt so good. Maybe inside Miyu’s butt would’ve been better but that was something that she could hopefully find out later. “I guess I had a sort of oopsie of my own, sorry about that. Just stay still like that, and I’ll clean you up properly this time.”

The fact that she came so quickly filled the air with a bit of awkwardness but as she headed over to her desk to grab the wet wipes she was supposed to use before, Illya’s foot knocked against one of the unopened gifts, namely the larger of the two boxes remaining. Chloe had mentioned wanting her to open it and Illya’s curiosity got the best of her as she couldn’t stop herself from gasping. Once again, she found herself thrown for a loop about whether or not Miyu’s accident was actually an accident. “Um, Miyu, are you sure that this all wasn’t planned by you and Chloe?”

“I-I thought I told you, it was an a-accident and I didn’t mean… to… Why do you have those…?” An already ridiculous situation was becoming even more ridiculous as it was all too obvious what Illya held in her hands, especially since the majority of the packaging was clear. To think she got herself into all of this just because Chloe manipulated her, a lot more than she expected too as her eyes danced along between the alternating blue and pink of the items in the package. “Did Chloe buy those diapers too? What are we even supposed to do with them.”

Maybe it wasn’t clear enough to Miyu but as Illya set down the diapers, she began to lift up the front of her panties, revealing a dark sticky stain on the front of her pink panties. “I sort of had an accident of my own too though, so in return for me changing you, we could actually put them to use. You wouldn’t mind doing that as well for my birthday, right, Miyu?” Pulling the birthday card was a little dirty after such a dirty display already, but Illya opened up the package and pulled out one of the diapers. Light pink leak guards and tapes with the rest being white was perfect for her as she held it in front of her chest.

Such an adorable display made it easy for Miyu to fall for it, more so since it was Illya asking her to do it. All of this stuff almost felt like too much but Miyu kept pushing forward because it was Illya, and if Illya wanted to be put in a diaper for her birthday, then Miyu was going to put Illya in a diaper for her birthday. “Lay on your bed and give me the diaper then, I think I’ve read something before on how to do it. And then I’d like a change myself, please.” Just a book that had been among various that she had read in the past, although the four-tape design confused her just a little before her more prodigal side got to work.

A bottle of baby powder was passed to her as well while Illya got herself comfy on the side of the bed, although perhaps she got herself a little in over her head as her hands nervously slid Illya’s panties off of her waist. The grinding from before had been one thing, but the front of Miyu’s panties couldn’t help but bulge out a little as she got a better look at Illya’s butthole and little cock, the latter now flaccid after getting so excited before. There wasn’t really much wiping to be done besides cleaning up a few sticking spots with the clean area of the panties, yet Miyu’s could feel how hot her face was the entire time and the embarrassment seemed to be shared between them. It almost felt like this was too mundane to be embarrassed about after the soiling and grinding but Miyu finally managed to slip the diaper under Illya’s butt. Her already snow-white butt got powdered up, leaving Miyu to try to fit the tapes around Illya’s soft thighs and waist as best as she could. “Does that feel good enough then? Or do you need me to readjust anything?”

It was already a pretty snug fit and Illya leaned up in bed before flashing a smile to Miyu. “It’s perfect, you did a great job. Thank you for the diaper change, Miyu~” Chloe must have gotten these custom-made or something with how snugly they fit, especially the appropriate colors of the padding. If pink was meant for her, then someone else was meant to fit into the blue ones. “Okay, and now your turn, Miyu. Just close your eyes and I’ll make sure to clean you up, alright?” With that, she was met with a nod from Miyu, leaving Illya to get some clean underwear for her friend.

Making her way over to her dresser, Illya’s thoughts went back to the package of diapers and just the thought of Miyu wearing one made her little dick try to stiffen up again. It was tough to tell just how much Miyu was into all of this but Illya kept pushing her luck while returning with the wipes and a lack of panties. Miyu’s panties were carefully removed and Illya made sure that Miyu wasn’t peeking, especially as she was finishing cleaning up and the silver-haired girl committed to her choice. Moving the ribbons away from her crotch, Illya unfolded the diaper and took a deep breath.

The change was going pretty well for Miyu but she couldn’t help but bolt up the moment that something crinkled under her butt. “Wait, when you said a change, I thought you meant panties. I put you in a diaper because it’s your birthday but why are you putting me in one too?” She tried to avoid all this infantile stuff, and yet going from poopy panties to a diaper was an easy way to make anyone feel like a baby. 

“It’s your birthday too, so we can both be diapered. I also don’t want you to have another accident, at least not without the proper protection. Don’t you want to be padded up with me?” This was easily a wonderful fantasy for her, just as the mushy grinding was, although there was a whole lot more to do in diapers. She already had one idea brewing, but that meant fighting a little to get this diaper taped onto Miyu. Good thing Miyu listened pretty well to her, and Chloe too since Illya had to guess that was how she got wrapped up in all of this. “If being padded together isn’t enough, then I’ll give you an extra special present, alright?”

The moment she got those words out, Miyu’s resistance faded, letting her throw on some powder before taping her friend into a similarly-designed diaper, only that the pink was replaced with a blue that was more appropriate for Miyu. With a few checks of the leak guards and waistband, Illya felt content with her diapering skills. “There, now how does that feel? Not as bad as you would’ve thought, right? Oh, and move back more onto the bed and close your eyes again, I have to get your present.”

As much as Miyu wanted to disagree because she was a fifth-grader wearing a diaper, she had to admit that this padding was actually pretty comfy. That didn’t make her any less embarrassed though since it felt like her face was as red as the ribbon that still covered her chest and abdomen. “It makes me feel like an infant, but maybe it’s not so bad. I’d still prefer to use a toilet though, so if I need to use the bathroom, I’m taking it off.” Still, Illya had mentioned a birthday gift for her, and while the diapering wasn’t quite what she was expecting, Miyu kept her hopes up for what Illya had in store for her now.

Calming herself and closing her eyes, Miyu did her best to keep them shut but her curiosity was a tough temptation to fight as she tried to listen to what was happening in the room. The crinkling from the diaper made Illya a lot easier to track than she expected, quietly waiting to hear the other girl go grab something but that never came. Instead, she intently listened to the crinkling go by the side of the bed before feeling some weight near her head, making sure to keep her eyes closed as she once again didn’t want to spoil a surprise. However, as something heavy fell by one side of her head and then the other, Miyu barely managed to open her eyes in time for her vision to be eclipsed by whiteness.

A lot of poofy, crinkling whiteness in particular, but her struggling under the mass proved futile when she realized what happened: Illya sat on her face with her diaper on. Miyu’s feelings were immediately conflicted since, on one hand, this was Illya sitting on her face, but on the other hand, there was still a diaper between Illya’s actual butt and her face. The former was still enough to stir up some feelings in her since the padding in the front of her diaper started to tighten. If only she could manage to say something but even she could hear how muffled her words were as Illya’s huge diaperbutt rested over her whole face.

“Surprise, Miyu!~ Hopefully, you can hear me back there but I had to wonder what would be good for you. After that accident and letting me diaper you though, it made me wonder if you might like this kind of stuff. I have my answer though.” With a lot of her weight focused on keeping her padded rear on Miyu’s face, Illya leaned over far enough to be able to feel Miyu’s. She started from where the padding was eclipsed by her thighs and slowly brought her hand along the front of it, targeting a specific small bulge. “You were flaccid during the change but what happened to make the front all stiff? Could it be this?” As she wiggled her butt around a bit on Miyu’s face, Illya managed to feel something stirring in the front, and so she continued to rub the front of the diaper while she got ready for the best part.

Even if she was a little bit of a quick shot herself as proven earlier, Illya had to wonder just how sensitive Miyu was, something that she was starting to see between a mix of rubbing the front of her diaper while Illya grinded back and forth on her face. This could be even better though and Illya did her best to relax before the excitement got her too nervous. If Miyu was loving this so much already, then all Illya had to do was start pushing.

The thick diaper almost completely encompassed the face of the girl on the bottom, and Miyu was almost glad since all that rubbing in such thick material was shamefully stirring up a naughty reaction. It almost felt as hopeless to try to hold it in as when she was in the box, and Illya had already done it too, so her resistance was wearing more and more away. Even her legs kicked a little in an attempt to contain the feeling but as Miyu got closer to the edge, her darkened vision suddenly turned a whole lot more brown and in that moment of feeling the burst of warmth as Illya made her diaper mushy on her face, her little cock burst and Miyu found her hips bucking. After being so against the thought of using her diaper or even pooping her panties in the first place, it took Miyu by surprise that she was orgasming to Illya packing her pampers on her face, and orgasming hard enough that she almost felt like passing out. Her thrashing legs went mostly limp and she couldn’t struggle very much, in addition to trying to stay still since even the smallest of movements around the front of her diaper reminded Miyu of how sensitive it felt. All from having Illya soil an infant’s undergarment on her face…

With how tuckered out she was, it took a few moments for her senses to return as the light of the room could once again be seen, namely so that she could see how Illya’s diaper was sagging quite a lot. The drooping diaper was only a few inches still from the front of her face despite Illya sitting up more than just a few inches. “Oh, sorry, what did you say again?” Getting over the euphoria of such a strong orgasm was tough and Miyu’s mind felt unclear, making it tough to focus a little.

“I was asking if you were alright but I can see you were certainly alright in your diaper.” The front of Miyu’s diaper was just slightly stained, certainly not yellow enough to be urine, and that only made it clearer what just happened. Illya felt more than satisfied with her surprise at least, both in managing to make Miyu cum in her diaper and having been able to fill her own diaper so much. There was so much back there to grope and Illya wished she had more time to indulge, whether in her own poopy underwear or seeing others soiling themselves. Either way, Illya was in a heaven of her own, but still grounded enough to check on her friend.

“Besides feeling really exhausted from all of that, I think I’m alright. I guess I had an accident like you did earlier though.” Hopefully, the sensitivity would calm down and she’d be able to move around, but for now, Miyu managed to sit herself up while Illya stopped straddling her. The loud plopping squish of the dirty diaper landing on the bed next to her almost made her cringe but if Illya really enjoyed this kind of stuff, then she’d have to get used to that sound. Still, as her mind became less foggy, one thought returned to her mind from her. If the big box had her in it, and the medium box had the diapers in it, then what about the smallest box? “Chloe said there was another box for you to open, right?”

“Oh right, makes you wonder what she has in store for us next.” Once more, Illya climbed over Miyu and for a moment, the latter had the stray thought of the diaper rubbing against her once again. Even after staining her diaper already in that fashion, Miyu almost felt greedy for wanting it more, wondering if she was starting to awaken to a fetish for this kind of stuff. That’d be interesting to explore, especially since she’d get to do it with Illya, but as for now, Miyu turned to look to see what got Illya so quiet after the rustling of opening the final box.

Of all the things for Illya to be holding up, it was a pair of onesies, one light pink and the other dark blue. The shades matched the diapers that both girls were wearing and Miyu caught the expectant look again in Illya’s eyes. “You don’t even have to ask, let me just get this ribbon off and you can help me into it.” If she felt infantile before, then this was on another whole level as Miyu until the red ribbons around her chest, only for Illya to replace them with the soft and surprisingly comfortable onesie. She even snapped all the buttons in place and calling herself an oversized baby was an understatement.

And, of course, as soon as she was about to ask Illya if she wanted help, she turned to see that Illya was already down to only her diaper. The immediate blush on her face made it feel like a shame to cover up Illya’s cute petite chest but matching together like this was turning out to be pretty adorable. Like a sort of warm, fuzzy feeling in her chest, but maybe she was just getting tired after such an eventful evening. That was obvious as Miyu took a big yawn, only to suddenly find something rubbery between her lips. Wait, when did she have a pacifier in her mouth?  
A quick look showed that Illya had one as well in her mouth, although hers matched her onesie while Miyu’s matched her own. “Aww, are you sleepy, Miyu? Good thing those were in the box too, maybe they’ll help us sleep together.” Illya seemed to be such a natural baby, already climbing in bed and under the covers while inviting Miyu under them. None of these things seemed to phase her, whether diapers or onesies or pacifiers, all while Miyu had to recollect herself a little from yet another surprise.

Maybe, just maybe, she shouldn’t think too hard about this one, and so she climbed under the covers with Illya. Softly sucking her pacifier while listening to Illya do the same, Miyu found herself enjoying all of this a lot more than she thought. There were a lot of things she was learning tonight, including that Illya was quite the clinger in bed since she could feel something mushy crinkling against her thigh.

Just as she was beginning to fade with Illya having already passed out, Miyu just barely made out the sounds of a door opening. Based on the look of the figure in the dark, Miyu could only guess that it was Chloe, especially when there was a brief flash of a phone’s brightness. She was saying something and it took all of Miyu’s effort to make it out, but she swore that she heard close say something like: “Oh my, that’s a longer video than I expected, hehe~” Oh well, she could deal with that tomorrow if she remembered but, for now, Miyu rested her head against Illya’s and her sleepiness overtook her as she contently smiled behind her pacifier.


End file.
